1. Field of the Invention
The present invention relates to a miniature and high performance antenna applicable to a radio communication apparatus and made up of a straight antenna rod and a coiled element.
2. Description of the Related Art
Portable radio communication apparatuses, including hand-held telephones, are extensively used today. To enhance portability, the casing of this kind of apparatus is decreasing in size and weight. An antenna small enough to be retracted even into such a small casing has been proposed in various forms. The prerequisite with the apparatus is that it can respond to a call originated on a remote station even when the small antenna is retracted into the casing. Further, there is an increasing demand for higher antenna sensitivity. In light of this, it has been customary to provide the apparatus with a built-in antenna in addition to the retractable antenna and to use them selectively. However, the problem with this approach is that the apparatus has a complicated and bulky construction. To eliminate this problem, when the antenna is retracted into the casing, a loading coil portion associated with the antenna may be directly fed to insure sensitivity, as taught in, for example, Japanese Patent Laid-Open Publication (Kokai) Nos. 1-101702 and 1-101703. Antennas aiming at miniaturization are disclosed in, for example, Japanese Patent Laid-Open Publication No. 3-245603 and EP Publication No. 0 467 822.
However, conventional antennas are complicated in structure and, therefore, difficult to produce, resulting in an increase in production cost. Moreover, a part of metallic members included in the antenna is exposed to the outside, impairing the appearance of the apparatus. In addition, when a part of the human body touches or even approaches the exposed portion of the antenna, the frequency changes.